<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>isBoolean</title>
</head>

<body>
    <script>
        const isBoolean = val => typeof val === 'boolean';
        document.writeln(`isBoolean(null)的结果是:${isBoolean(null)}。isBoolean(false)的结果是:${isBoolean(false)}`)
    </script>
</body>

</html>